The present invention relates to lubricants, and more particularly to hydrocarbon lubricants containing deuterium.
Oxidation is a serious problem in the use of hydrocarbon lubricants. When hydrocarbons are oxidized by the ambient air, acidic products form which deteriorate the lubricant. If the hydrocarbon is being used to lubricate metal surfaces, these acidic products of oxidation also corrode the metal. In addition, oxidation thickens the lubricant, so that lubricant flow is thereby impaired. Poor oxidation resistance thus means a shorter effective life for the lubricant. In contrast, a lubricant with good oxidation resistance can withstand higher temperatures and has a longer effective life. As a result, there is less downtime and teardown of equipment utilizing lubricants having good oxidation resistance.
One practice to improve the oxidation resistance of a hydrocarbon lubricant has been deuteration, wherein the hydrogen atoms covalently bound to carbon atoms in the hydrocarbon molecule are replaced with deuterium atoms. Deuterium is a non-radioactive isotope of hydrogen which is sometimes called heavy hydrogen. The carbon-deuterium chemical bond is stronger, more stable and reacts more slowly than the carbon-hydrogen chemical bond, so that the rate of oxidation for a deuterocarbon (partially or fully deuterated hydrocarbon) lubricant is substantially less than that for an undeuterated hydrocarbon lubricant. In addition, deuteration of a lubricant does not affect most of the lubricant's other chemical properties such as lubricity, which would be affected if oxidation resistance additives or inhibitors were used with a lubricant instead of deuteration. Deuteration of high molecular weight hydrocarbons can be accomplished by the method disclosed in U.S. Pat. Nos. 3,746,634 and 3,876,521 to Joseph G. Atkinson et al, wherein deuteration is effected with deuterium gas in the presence of a Group VII or VIII metal catalyst at a temperature between about 100.degree. and 300.degree. C. The deuterium gas used to exchange with the hydrogen atoms in the hydrocarbon is generally obtained from the electrolysis of heavy water (D.sub.2 O) which is present in ordinary water at 0.004% concentration levels. Isolating and obtaining a supply of heavy water and deuterium gas is expensive, so that the deuteration of hydrocarbons is expensive.